[pbhjpbhj]

The question still stands. Why interrupt the road traffic if there are no pedestrians waiting? It's possible to answer that "for flow control" but I'd warrant that's not an effective proposition for the majority of junctions.

I didn't see this specific question addressed in the OP so it's quite possible it was simply glossed over to provide a simplified answer or the reporter worked around it to make it easier to express the sequence.